The present invention relates to spindle motor control in disk drives, and more particularly, to regulating variations in spindle motor speed.
In many processing and computing systems, magnetic data storage devices, such as disk drives are utilized for storing ever-increasing amounts of data per unit storage area of the disk drive. A typical disk drive includes a spindle motor having a rotor for rotating a data disk, and an actuator for moving a head carrier that supports transducer (read/write) heads radially across the disk to write data to or read data from concentric data tracks on the disk. A motor controller regulates drive currents to the motor to rotate the disk.
The amount of the xe2x80x9crawxe2x80x9d capacity of a disk can be represented as the product of the allowable bit density (i.e., the density of flux changes along a track, such as bits per inch), the allowable track density (e.g., tracks per inch), and the total usable area of the disk. The ratio of user data that can be stored on the disk compared to the raw capacity (i.e. data format efficiency) is less than 100% because a portion of the raw capacity is devoted to servo information, servo addresses and data identification. Further, another portion of the raw capacity is devoted to inter-sector xe2x80x9cpaddingxe2x80x9d such as guard-bands and buffer zones. In particular, a buffer zone is provided between sequential data sectors on each track to protect against overwriting of user data on the disk due to spindle-speed variations relative to a reference clock for writing data. This is because during a data-write operation the spindle motor speed can vary, and if the variance is substantial relative to the reference clock, data will be written out-of-position on a track, overwriting the preceding or succeeding data sectors on that track.
With the ever-increasing need for additional data capacity for storing user data in disk drives, some disk drives utilize increased flux transition density within each data track on the data disks to increase the data format efficiency. Further, the data tracks are made narrower and recorded closer together. However, the increasing bit and track densities require complex transducer heads and data transfer channels. As such, in some disk drives the data capacity is increased by reducing the inter-sector padding to improve the disk""s data format efficiency and to increase the data capacity of the disk drive for storing user data. To prevent data overwrites due to reduced padding, the spindle speed is monitored based on rotor position information from the motor, such as spindle index mark, to reduce spindle speed variations, and the transducer position on each track is detected to inhibit data-writes during out-of-speed conditions. A sensor detects the time of arrival of the spindle index mark once per revolution, and that information is used by a spindle motor controller to provide motor currents to attempt a nearly uniform rotational speed.
However, a major disadvantage of such disk drives is that the motor controller regulates the spindle motor current based on spindle position information detected once per revolution. This sparse, once per revolution, position information provides for only very coarse speed regulation and, therefore, reduction in spindle speed variation is limited. As such, the inter-sector padding can only be marginally reduced. There is, therefore, a need for a method and apparatus for regulating the spindle speed in a disk drive which provides for substantial reduction in inter-sector padding, thereby increasing the data capacity of the disk drive.
The present invention satisfies these needs. In one embodiment, the present invention provides a spindle motor control for a disk drive including a spindle motor for rotating a data disk at a desired rotational speed precisely regulated by the spindle motor control, and a data transducer head positionable relative to selected ones of a multiplicity of concentric data tracks formed on a data storage surface of the disk drive. The concentric data tracks are periodically interrupted by a plurality of servo sectors per rotation, where each servo sector recorded with head position information. The spindle motor control includes: (a) a servo detector for detecting the head position information in at least one servo sector on a selected track under the transducer head in relation to a timing signal at a reference frequency; (b) a position detector for determining the circumferential position of the detected head position information on the selected track in relation to the timing signal; and (c) a controller for controlling the rotational speed of the spindle motor as a function of said circumferential position, to regulate the circumferential position of the transducer in relation to the servo sectors on the data tracks.
The head position information in each servo sector includes servo burst signals recorded at said reference frequency, and the servo detector detects at least one servo burst signal in a servo sector on the selected track via the transducer head and generates a readback signal. The position detector can further include a burst phase detector for determining a burst phase of the readback signal relative to the timing signal, said burstphase comprising the phase-angle between the readback signal and the timing signal. The controller controls the rotational speed of the spindle motor to regulate said burst phase, such that the frequency of rotation of the data disk is a function of the reference frequency.
In one embodiment, each servo burst signal includes at least one substantially cyclical signal at said reference frequency, wherein the servo detector further includes sampling means for sampling the cyclical signal a multiplicity of times for at least one cycle of the cyclical signal at a sampling rate related to the reference frequency to provide data samples such that said readback signal includes said data samples. The burst phase detector can include means for performing a Fourier transform of the data samples to provide a phase of the cyclical signal as the burst phase. Preferably, the means for performing the Fourier transform performs a single-frequency Fourier transform of the data samples at said reference frequency to provide a phase of the cyclical signal as the burst phase.
In one example, the sampling means samples the cyclical signal at least at about 0, 90, 180 and 270 degrees for at least one cycle of the cyclical signal. The position detector includes: (i) a first difference means for subtracting the data sample at 180 degrees from the data sample at 0 degrees to generate a first difference value, and (ii) a second difference means for subtracting the data sample at 270 degrees from the data sample at 90 degrees to generate a second difference value. The burst phase detector includes means for calculating the arc-tangent of the first and the second difference values to ascertain said burst phase. Further, the controller controls the rotational speed of the spindle motor to achieve a desired burst phase such as zero.
In another aspect the present invention provides a disk drive including said spindle motor control. Yet, in another aspect the present invention provides a method of performing spindle speed control in the disk drive by performing steps including: positioning the transducer head over a selected track; detecting the head position information in at least one servo sector on the selected track under the transducer head in relation to a timing signal at a reference frequency; determining the circumferential position of the detected head position information on the selected track in relation to the timing signal; and controlling the rotational speed of the spindle motor as a function of said circumferential position, to regulate the circumferential position of the transducer in relation to the servo sectors on the data tracks.